The invention generally relates to techniques for analyzing the electrical activity of the heart and for administering electrical therapy to the heart.
Atrial fibrillation (xe2x80x9cAFxe2x80x9d) is a heart arrhythmia wherein the atria of the heart beat chaotically thereby providing generally poor conduction of blood into the ventricles of the heart and hence reducing the flow of blood throughout the body. AF, by itself, is typically not fatal. However, AF has been shown to lead to long term health problems such as increased risk of thrombolytic stroke. AF can also cause reduced cardiac efficiency, irregular ventricular rhythm and unpleasant symptoms such as palpitations and shortness of breath.
Hence, it is highly desirable to terminate AF. One technique for terminating AF is to administer an electrical cardioversion pulse to the atria of the heart. The cardioversion pulse, if successful, terminates the chaotic pulsing of the atria and causes the atria to resume a normal beating pattern. In an attempt to insure success, the amount of electrical energy in the cardioversion pulse is set to an amount greater than an atrial defibrillation threshold (xe2x80x9cDFTxe2x80x9d) which represents the minimum amount of energy that typically needs to be applied to the heart to terminate AF. The atrial DFT may vary from patient to patient. To determine the atrial DFT for a particular patient, AF is typically induced within the patient, then cardioversion pulses of varying strengths are applied to determine an amount of energy that can reliably defibrillate the atria of the particular patient.
Patients prone to AF may have an implantable cardioverter defibrillator (xe2x80x9cICDxe2x80x9d) implanted therein capable of detecting AF and automatically administering one or more cardioversion pulses to terminate the AF. The atrial DFT for the patient is programmed into the ICD so that a controller of the ICD can determine the appropriate amount of electrical energy to administer within each cardioversion pulse. Typically, about two joules of energy is administered within each pulse. A typical ICD is also capable of detecting a wide variety of other heart disrythmias, such as ventricular fibrillation (VF), and for administering appropriate therapy as well. For VF, the ICD administers a stronger defibrillation pulse sufficient to overcome a ventricular DFT, on the order of ten to twelve joules of electrical energy, directly to the ventricles of the heart.
Although cardioversion pulses have been found to be effective for terminating AF and other atrial tachyarrhythmias within many patients, the cardioversion pulses can be quite painful to the patient. One reason the cardioversion pulses are painful is that the patient is typically conscious and alert at the time the pulse is administered. In contrast, the much stronger defibrillation pulse for terminating VF is typically not administered until the patient has lost consciousness and hence the patient may feel only residual chest pain upon being revived. Because AF is not usually immediately life-threatening, painful shocks for its treatment may be perceived by patients as worse than the disease itself and therefore not tolerated.
Thus, it is highly desirable to provide a technique for reducing the strength of the electrical cardioversion shock to thereby reduce the amount of pain induced in the patient, while still providing a sufficient amount of electrical energy to reliably defibrillate the atria of the heart. Another significant advantage of reducing the electrical energy per cardioversion pulse is that the lifetime of the power supply of the ICD is thereby significantly increased.
It has been found that certain shocking electrode locations and cardioversion waveforms lead to decreased atrial DFT""s. To prevent the cardioversion pulse from inadvertently triggering a VF, the cardioversion pulse is timed so as to occur during a ventricular refractory period occurring immediately subsequent to a contraction within the ventricles. To this end, the ICD also examines the IEGM to detect R-waves representative of contractions within the ventricles and times the application of the cardioversion pulse to occur during the ventricular refractory period.
Another method of cardioversion employs a train of sequential discrete pulses each having a considerably lower energy level than a single cardioversion pulse. Although these various techniques are helpful in reducing the amount of electrical energy per cardioversion pulse, considerable room for improvement remains.
Many of the concerns arising with respect to administering cardioversion pulses to terminate AF also apply to administering cardioversion pulses to terminate ventricular tachyarrhythmias. Heretofore, most techniques, which attempt to reduce the energy per cardioversion pulse are directed to selecting an optimum location for electrodes employed in administering the pulse. Other techniques have been directed to selecting optimal cardioversion waveforms.
For at least the foregoing reasons, it is highly desirable to provide techniques for reducing the strength of atrial and ventricular cardioversion pulses, particularly defibrillation pulses, while still achieving a high likelihood of success, and aspects of invention are directed to these ends.
Insofar as other forms of electrical cardiac therapy are concerned, such as anti-bradycardia pacing, a reduction in the strength of the electrical therapy while still achieving a high likelihood of success is also beneficial. Accordingly, aspects of the invention are also directed to permitting a reduction in the strength of other forms of electrical cardiac therapy besides cardioversion therapy.
In accordance with one aspect of the invention, a method is provided for applying an electrical pulse to a heart using an implantable cardiac stimulating device connected to the heart for terminating atrial fibrillation within the heart, wherein the pulse is applied based upon detection of a period of natural electrical coherence in the atria.
In accordance with the method, atrial fibrillation is detected within the heart. Then, a period of natural electrical coherence is detected among a plurality of separate locations within the atria of the heart. An electrical pulse is generated for applying to the heart at a time selected based upon the period of natural electrical coherence. Some of the plurality of locations may be, for example, within the left atria whereas others are within the right atria. As another example, the plurality of locations all may be within the left atria, but located separately from one another. The pulse may be applied, for example, during the period of electrical coherence, immediately after the period, or only after several consecutive periods of coherence have been detected. In any case, it is believed that the strength of the cardioversion pulse can be reduced as compared to pulses administered without regard to natural electrical coherence, while still achieving the same likelihood of successful cardioversion.
In accordance with another aspect of the invention, a method is provided for analyzing the electrical activity of the heart using an implantable medical device connected to a heart. In accordance with the method, electrical signals are detected at a plurality of locations within the heart. The electrical signals are compared to identify one or more periods of natural electrical coherence among the signals. Some of the plurality of locations may be, for example, within the left atrium of the heart whereas others are within the right atrium.
In an exemplary embodiment, wherein the implantable medical device includes a cardiac stimulating device, therapy is then selectively administered to the heart at a time based upon detection of the period of natural electrical coherence. The electrical therapy may be, for example, atrial or ventricular cardioversion therapy or pacing therapy. By administering therapy based upon detection of natural electrical coherence, it is believed that the therapy can be more effective.
Apparatus embodiments of the invention are also provided. Other objects, advantages and features of the invention are either specifically described below or will be apparent from the descriptions which follow and from the drawings provided herewith.